Hitchhiker's Guide to Rukl Chart 18

Bright crater Aristarchus is visible to the naked eye as an albedo
feature when it is well illuminated. A system of rilles starts north
of it, and extends to the north.

3/9/98: Schroter's Valley was just barely all in sunlight -- the region
between the Cobra Head and Herodotus was still darkly shadowed by
nearby high terrain. I could see Rimae Aristarchus, and associated
rilles I, III, and VI. Rille III was most prominent northwest of
Prinz -- I could not see any of III, IV, or V where they lie parallel,
close to 27 N 46 W.

Schroter's Valley (Vallis Schroteri) starts northward slightly north
of crater Herodotus, then bends through nearly 180 degrees to the east
before opening out onto Oceanus Procellarum. I have seen it well in as
little as 55 mm aperture.

A horseshoe-shaped, sharp-edged canyon which seems
to pass underground as it exits Herodotus, then emerges onto the
surface and fans out as it makes its 180-degree bend.

Schroter's Valley does not begin to be visible until the area where
it lies is well past the terminator. Just before sunrise on the valley
itself, Rupes toscanelli is obvious, but look for a small but prominent
trough which bisects a small hill north of R. toscanelli.
The trough is unnamed on Rukl, but is drawn just over the "50 W"
on chart 18.

Schroter's Valley (David North <d _at_ timocharis.com>)

Schroter's Valley (Vallis Schroteri in the bogus latinate hokum the
official bodies have incorporated) "begins" in a highland, as does it's
smaller twin, Rima Birt. Since the valley looks like a snake, the
elongate depression where it begins was nicknamed the "Cobra Head" for
reasons obvious to anyone observing it in reasonable seeing.

Current theory states that the entire valley, including the head, are a
collapsed lava tube -- a course lava found from the "Cobra Head" through
the highlands and to its eventual terminus near the lowland mare
material. After the lava drained, it is presumed the tube collapsed from
the weight of the material above, leaving the trench as we see it. The
"head" was formed due to a larger collapse into the chimney from which
the lava emerged from a deeper source.

Such selenographic processes are not yet well enough understood to say
with any certainty if that is indeed the process that took place, or
from what level the lava originally began to rise. The curious nature of
the "island" in which Schroter's Valley is found adds further fuel to
the speculative fires; it's a curious area of isolated highland in the
midst of large maria.

Rima Marius (JRF <freeman _at_ netcom.com>)

This narrow sinuous rille wends across Oceanus Procellarum south of
Aristarchus and Herodotus.

Rima Marius (David North <d _at_ timocharis.com>)

... out of the corner of my eye, I spotted a filigree of light on
old Procellarum -- a faint wisp, a hint of a line. Very intriguing. So I
hunted the area, patiently, and slowly but surely a story unfolded, an
image of light rather than darkness... it was Rima Marius! This feature
is, at least to me, very elusive. But for the first time I recall, I was
tracing out almost the entire length, but illuminated! It was a *bright*
line on the darker floor; already the sun was reflecting from the
interior side of this shallow trench rather than casting a shadow from
its lip.

Possibly the interior matter is considerably brighter than the
surrounding mare material; I don't know. That would explain the
extraordinary contrast, and there's some small reason to believe the
underlying material in that area could be intrinsically bright, with
Aristarchus so nearby. But that would also imply a certain degree of
youth -- unlikely in my understanding that rimae are largely old
features. On the other hand, after forming there is some collapse of the
sides of the walls, and perhaps some of this "mass wasting" took place
relatively recently..? Jarred loose by the impact that formed
Aristarchus?

And there was a lesson for me: just because the mapmaker draws it
dark doesn't mean it will be when you see it. I should know better by
now having seen this kind of thing before, but I don't. Ah, well.

The rille itself is a prototype "sinuous," bending throught three
distinct arcs somewhat reminiscent of the profile of a face from the
bridge of the nose to the chin. Most of this showed well in the
telescope, save the thinnest part of the end, which eluded me (the rille
goes a bit further past Marius B than I noted). It's graceful shape
outlined against the dark floor was very attractive of itself, even
without the excitement of the hunt. This was clearly the best sighting
I've ever had of it, and I have to say it's much more appealing when the
majority of it is visible -- rather than hunting little bits and dabs in
shakier seeing or poorer light.